Adaptive torque control of electro-rheological fluid brakes used in active knee rehabilitation devices

This paper describes the development of an adaptive nonlinear PI torque control for electro-rheological fluid (ERF) based variable resistance brakes that are used in compact and portable rehabilitation devices. The electrorheologic fluid (ERF) brake concepts are introduced and previous work performed with a non-linear PI control on ERFs is tested and analysed. The response of ERF brake systems to this non-linear PI torque control, that utilizes an inverse model, is enhanced through the addition of two key components, a step logic function and an adaptable B-spline based algorithm. The description of each is provided along with tests verifying their effectiveness. In addition, the controller´s response to disturbances is provided. The effectiveness of the control is validated through testing on two different electro-rheological fluid based brakes